1. Field of the Invention
The present invention is related to the field of electrode apparatuses for stray field radio frequency (xe2x80x9cRFxe2x80x9d) heating.
2. Discussion of the Background
A conventional electrode apparatus for stray field heating typically includes at least two parallel electrodes. The electrode apparatus is electrically connected to an RF generator that generates an RF signal. When the RF generator generates an RF signal, an RF field is generated between the two electrodes and a stray RF field is also radiated from the electrodes. The RF field is typically strongest in the region within the overlapping space between the electrodes, with a stray component of the field extending beyond the overlapping area of the electrodes. Stray field RF heating refers to the technique of heating a material by exposing the material to the generated stray field.
In one aspect, the present invention provides an RF heating system for generating precision stray RF fields that can be used to heat materials. The RF heating system includes an RF power supply for generating RF signals and an electrode apparatus that is coupled to the RF power supply. An electrode apparatus according to the present invention has many advantages over existing electrode apparatuses. For example, the electrode apparatus is easier to manufacture, easier to manufacture duplicate electrode systems, easier to control the manufacturing tolerances on the electrode system, and easier to correctly place and design the resulting RF stray field. Other advantages exist.
According to one embodiment, an electrode apparatus of the present invention comprises two elements: a first element and a second element. The first element and the second element are each energized by a radio frequency signal that is typically at a phase angle of 0xc2x0 and 180xc2x0 respectfully, to produce a voltage potential between the electrodes that varies between zero and a maximum potential at the frequency provided by the power supply. In addition, the first element could be energized by a radio frequency signal and the second element could be equivalent to ground, still providing a voltage potential between the electrodes that varies at the frequency of the source supply.
In one embodiment, the first element comprises a first elongated member and a second elongated member. The first element further comprises an elongated electrode having one end connected to the first elongated member and the other end connected to the second elongated member. The elongated members and the elongated electrode are preferably formed from a single mass of material (such as, but not limited to, a copper sheet or plate), but this is not a requirement.
The second element comprises a base and an electrode plate that is connected to and extends outwardly from a surface of the base. The electrode plate is rectangular in shape having two lateral sides and a distal side. Like the first element, the second element is preferably formed from a single mass of material, but this is not a requirement.
The first element and the second element are positioned such that the elongated electrode and the electrode plate are aligned so that, when the RF power supply produces an RF signal, an RF field is generated between the elongated electrode and the electrode plate, and a stray RF field radiates from the elongated electrode and the electrode plate. In one embodiment, the first element and the second element are positioned such that the elongated electrode and the electrode plate are spaced apart and interdigitated or interlaced or xe2x80x9claterally adjacentxe2x80x9d such that the elongated electrode is not directly over any portion of the electrode plate. That is, the distal side of the electrode plate runs substantially parallel with the elongated electrode and is spaced apart from the elongated electrode. Preferably, the distance from the top surface of the elongated electrode to the surface of the base is equal to or about equal to the height of the electrode plate, but this is not a requirement.
Advantageously, the first element may include a plurality of elongated electrodes. Each of the plurality of elongated electrodes having one end connected to the first elongated member and the other end connected to the second elongated member. Preferably, the plurality of elongated electrodes are evenly spaced apart and are parallel with each other. In this embodiment, the second element includes a plurality of electrode plates that are attached to and extend outwardly from the surface of the base. Like the elongated electrodes, the electrode plates are also preferably spaced evenly apart. In this embodiment, the first element and the second element are aligned so that the elongated electrodes and the electrode plates are interdigitated. Preferably, the distance from the top surface of an elongated electrode to the surface of the base is equal to or about equal to the height of the electrode plate(s) that are adjacent to the elongated electrode.
In one embodiment, the RF power supply includes an RF generator, an impedance matching circuit and an above described electrode apparatus. In this embodiment, the first element of the electrode apparatus is connected to a first node within the impedance matching circuit and the second element of the electrode apparatus is connected to a second node within the impedance matching circuit. In one embodiment, an element having an inductance (e.g., a conductive coil) is connected between the first node and the second node.
In another embodiment, the second element of the electrode apparatus is placed within a housing and the first element rests on a surface of the housing. The housing is preferably constructed from a non-conducting or low dielectric constant or low dissipation factor material such as, but not limited to Teflon(copyright) (polytetraflouroethylene), polypropylene, polyethelene, Kapton(copyright), and polystyrene.
In another aspect, the invention provides an electrode apparatus for generating stray fields that includes an elongated electrode and an electrode plate having a first face and a second face. The first face of the electrode plate faces in a direction that is substantially perpendicular to the longitudinal axis of the elongated electrode. The elongated electrode is spaced apart from the first face of the electrode plate. The height of the electrode plate is greater than the thickness of the elongated electrode. And the length of the electrode plate is shorter than the length of the elongated electrode.
In another aspect, the invention provides a method for making a product, wherein the product has one or more components. The method includes the steps of: generating a stray field using one of the electrode apparatuses described above and exposing a component of the product to the stray field for the purpose of heating the component. The component may be an adhesive that heats when exposed to certain RF fields or any other component.
The above and other features and advantages of the present invention, as well as the structure and operation of preferred embodiments of the present invention, are described in detail below with reference to the accompanying drawings.